Mario Pineida's stunning late goal saw Independiente del Valle to a 1-0 victory at home to Estudiantes in the Copa Libertadores on Thursday.
Pineida struck in the 80th minute at the Estadio General Ruminahui del Valle de Los Chillos in Sangolqui, Ecuador.
Estudiantes, four-time champions, need a win when they host the second leg on February 12.
The Argentines looked set to hold on for a draw away from home until Pineida rifled in the winner.
The 22-year-old cut inside from the left, holding off a marker before firing into the top corner from 25 yards to help Independiente del Valle take a huge step towards the group stages.
Nacional, three-time winners of the tournament, went down 1-0 at Palestino.
Diego Rosende was the hero for the Chilean hosts, netting in the 70th minute in Santiago de Chile.
But a 35th-minute red card to Nacional defender Diego Polenta proved costly for the visitors, who were eventually punished.
Rosende found the bottom corner from just inside the area after a nice touch from Diego Chaves set up the chance.